In general, sensor elements are electrically connected by an external measuring system. In this context, it is often provided that the measuring system switches over between different measurements and operating states of the sensor element, using different circuit states. The switching-over may take place periodically in a predefined order, so that a circuit state is always set at the same switching position or positions of a measuring period.
Sensor elements, on which such cyclically alternating, protective circuits are provided, include, for example, wide-range lambda probes, as are used for monitoring the composition of the exhaust gas of internal combustion engines for maintenance of limiting values. The correct functioning of such exhaust-gas sensors and, in particular, their resistance to aging, as well, are a strong function of their protective electronic circuit. The functional blocks of such a protective circuit are described, for example, in the document DE 10 2006 061 565 A1.
In the document DE 10 2008 001697 A1, an improved wiring configuration is described, which allows, in addition to the operation of the exhaust-gas sensor, information about the operating state of the wide-range lambda probe used there as an exhaust-gas sensor to be acquired, to be stored, and to be retransmitted to a superordinate engine control unit via a digital interface. This set-up allows a diagnosis of the lead-wire connections between the protective circuit and the wide-range lambda probe, for a short circuit and a break, as well as for maintenance of permissible voltages at the terminals. The operation readiness of the exhaust-gas analyzer probe may be detected, and its electrode polarization and the aging may be continuously monitored. In order to perform these measurements and to set the different operating states, the wide-range lambda probe is variably connected electrically in successive circuit states of the control electronics, and accordingly acted upon electrically in a variable manner. In this context, previous circuit states may influence measurements. For example, a circuit state may produce unwanted polarization of a Nernst cell of the wide-range lambda probe, which, in a subsequent circuit state, may lead to falsification of the measured value of the Nernst voltage at the Nernst cell. If the circuit states are selected periodically, then the influence on the measured values is also periodic. Today, such measuring errors are mostly corrected using a low-pass filter, through which, however, the signal dynamics are reduced.